A separate-type air conditioner conventionally includes a refrigeration circuit shown for example in FIG. 23. The refrigeration circuit includes a compressor 201, an outdoor coil 202, an expansion valve 203, and an indoor coil 204. The compressor 201 and the outdoor coil 202 are accommodated in an outdoor unit 205. The expansion valve 203 and the indoor coil 204 are accommodated in an indoor unit 206. An electric expansion valve, such as that shown in FIG. 24, is used as the expansion valve 203.
The electric expansion valve includes a valve body 210, in which an inlet port 211 and an outlet port 212 are formed. A valve chamber 213 and a refrigerant flow passage 214 are formed in the valve body 210. The valve chamber 213 and the refrigerant flow passage 214 communicate the inlet port 211 with the outlet port 212. The valve body 210 has a partition wall 216 in which a valve hole 217 is formed. A valve member 215 is accommodated in the valve chamber 213 in a manner that its distal end faces the valve hole 217 of the partition wall 216. The valve member 215 has a distal end portion that defines a tapered portion 218. A throttle 219 is formed by the tapered portion 218 and the valve hole 217. The valve member 215 advances and retracts with respect to the valve hole 217 when driven by a drive unit, such as a pulse motor (not shown). The advancement and retraction of the valve member 215 adjusts the open degree of the valve hole 217 (the throttling amount of the throttle 219).
A cooling operation cycle in the separate-type air conditioner will now be described with reference to FIG. 23. High-pressure gas refrigerant compressed by the compressor 201 first flows to the outdoor coil 202, where the refrigerant, which exchanges heat with the ambient air, condenses and liquefies. The liquid refrigerant enters the valve body 210 of the expansion valve 203 via a liquid tube 207 and the inlet port 211. The refrigerant entering the valve body 210 flows to the indoor coil 204 via the throttle 219 and the outlet port 212. The refrigerant sent to the indoor coil 204, which exchanges heat with the indoor air, evaporates and vaporizes into low-pressure gas refrigerant, which returns to the compressor 201.
In the separate-type air conditioner, bubbles may be formed in the liquid tube 207 connecting the outdoor coil 202 and the expansion valve 203 depending on the installment condition or driving condition of the air conditioner. If the bubbles coalesce and produce a slug flow or plug flow in the refrigerant, the refrigerant may flow alternately in a liquid phase and in a gaseous phase through the throttle 219. This increases velocity fluctuations and pressure fluctuations in the refrigerant. In this case, the refrigerant flow may generate noise near the outlet of the expansion valve 203. The same problem also occurs in a heat-pump air conditioner during a heating operation.
To reduce pulsations in the refrigerant flow, in one conventional method (conventional method A), an aggregate of narrow passages near the outlet of a throttle and rectifies the refrigerant flow. More specifically, patent document 1 discloses a structure in which a porous member or an aggregate of capillaries is arranged near a throttle. Patent document 2 discloses a structure in which a honeycomb pipe formed by a bundle of capillaries or a molecular sieve is arranged near the outlet of a throttle. Further, another conventional method (conventional method B) changes the shape of a flow passage near an outlet of a throttle. More specifically, patent document 1 discloses a structure in which the inner diameter of the vicinity of an outlet of an orifice, which forms a valve hole, is formed so as to increase in steps or in a continuous manner by providing a tapered form and arranging grooves in the inner surface of the valve hole. A further conventional method (conventional method C) forms a throttle with a two-step structure and generates an intermediate pressure between the two steps to disperse the kinetic energy of the refrigerant. More specifically, patent document 3 discloses the structure in which a two-stepped orifice is arranged in a throttle of a refrigerant flow passage. Further, patent document 4 discloses another method (conventional method D) in which a throttle has a single-step structure, with the throttle being formed by a plurality of refrigerant flow passages.
Patent Document 1: Japanese Laid-Open Patent Publication No. 7-146032
Patent Document 2: Japanese Laid-Open Patent Publication No. 11-325658
Patent Document 3: Japanese Laid-Open Patent Publication No. 5-322381
Patent Document 4: Japanese Laid-Open Patent Publication No. 5-288286